Hypersomnia is a disorder characterized by excessive sleepiness, extended sleep time in a 24-hour cycle, and the inability to achieve the feeling of refreshment that usually comes from sleep. There are two main categories of hypersomnia: primary hypersomnia (also called idiopathic hypersomnia) and recurrent hypersomnia (also called primary recurrent hypersomnia). Both have the same symptoms, but differ in frequency of occurrence.[1]

Note: In the proposed 5th edition of the Diagnostic and Statistical Manual of Mental Disorders, due for publication in May 2013, hypersomnia is reclassified under Sleep-Wake Disorders as Hypersomnolence, of which there are several subtypes.[2] Primary hypersomnia is reclassified as Major somnolence disorder.[3] Idiopathic hypersomnia is not included. As of November 2012, the draft diagnostic criteria for DSM-5 are still in flux and the specific criteria text has been removed from public view on the DSM-5 Development site.[4]

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According to the U. S. National Institute of Neurological Disorders and Stroke:

"Hypersomnia is characterized by recurring episodes of excessive daytime sleepiness (EDS) or prolonged nighttime sleep. Different from feeling tired due to lack of or interrupted sleep at night, persons with hypersomnia are compelled to nap repeatedly during the day, often at inappropriate times such as at work, during a meal, or in conversation. These daytime naps usually provide no relief from symptoms. Patients often have difficulty waking from a long sleep, and may feel disoriented. Other symptoms may include anxiety, increased irritation, decreased energy, restlessness, slow thinking, slow speech, loss of appetite, hallucinations, and memory difficulty. Some patients lose the ability to function in family, social, occupational, or other settings. Hypersomnia may be caused by another sleep disorder (such as narcolepsy or sleep apnea), dysfunction of the autonomic nervous system, or drug or alcohol abuse. In some cases it results from a physical problem, such as a tumor, head trauma, or injury to the central nervous system. Certain medications, or medicine withdrawal, may also cause hypersomnia. Medical conditions including multiple sclerosis, chronic fatigue syndrome, depression, encephalitis, epilepsy, or obesity may contribute to the disorder. Some people appear to have a genetic predisposition to hypersomnia; in others, there is no known cause. Hypersomnia typically affects adolescents and young adults, although the most common causes of the condition for the two age cohorts differ."[5]

Those who suffer from hypersomnia have recurring episodes of excessive daytime sleepiness (EDS), which is different from feeling tired due to lack of or interrupted sleep at night. They are compelled to nap repeatedly during the day, often at inappropriate times such as at work, during a meal, or in conversation. These daytime naps usually provide no relief from symptoms.

Typically, hypersomnia is first recognized in adolescence or young adulthood.[5] Patients with hypersomnia often experience prolonged night sleep and have difficulty waking from extended sleep episodes, feeling disoriented upon doing so. This condition is known as sleep inertia or, more descriptively, as sleep drunkenness.[6] Other symptoms may include anxiety, increased irritation, decreased energy, restlessness, slow thinking, slow speech, loss of appetite, hallucinations, memory difficulty and difficulty regulating body temperature.[7] Some patients lose the ability to function in family, social, occupational or other settings.[8] These symptoms are present in both types of hypersomnia. A sufferer of primary hypersomnia displays these symptoms continually for months or years.[8] Recurrent hypersomnia is characterized by recurring periods of symptoms many times throughout the year mixed with periods of normal sleep-wake cycles. Kleine-Levin syndrome is the most well-known form of recurrent hypersomnia, though it is very rare; sufferers often sleep up to eighteen hours a day and yet do not feel refreshed upon waking.

People who are overweight may be more likely to suffer from hypersomnia. This can often exacerbate weight problems as excessive sleeping decreases metabolic energy consumption, making weight loss more difficult. However, it is also the case that sleep disorders of this nature provoke or initiate weight gain due to a tendency to attempt to manage low energy levels by eating non-complex carbohydrates.

Nevertheless, treatment for primary (or idiopathic) hypersomnia is far from satisfactory. CNS stimulants tend to be less effective for hypersomnia than they are for narcolepsy and may be less well tolerated.[8] In addition, stimulants provide diminished returns when taken for a period of years, let alone a period of decades. The negative side effects of stimulants, such as hypertension, are also of concern.

A 2012 study found that flumazenil provides relief for some patients whose CSF contains an unknown "somnogen" that enhances the function of GABAA receptors, making them more susceptible to the sleep-inducing effect of GABA. For one patient, daily administration of flumazenil by sublingual lozenge and topical cream has proven effective.[12]